What are the steps to unzipping/rezipping the Settings.sts file?

I am having trouble getting the edited sts file to work. Last month, I unzipped it, made a minor edit, re-zipped it, changed it to the .sts file extension and it works fine.

This week, I copied the working sts file and made a minor edit. Now, I can't get it to work. When I select this sts file from the Settings File drop-down in the Publish dialog box, the message "Failed Parsing Setting File" appears.

It fails even if I simply unzip/rezip the working sts file. No changes to the contents of the Settings file, just unzip, rezip and it fails. 

Maybe it's something about how I'm unzipping/rezipping? I might have done it differently a month ago. Do you change the sts file extension to .zip before you unzip? Do you use the zip or 7z utility or something else to unzip? To re-zip? 

I've tried all variations with no luck. I'd appreciate any help! Under a deadline...of course!

FYI, FM 13.0.2.433. Creating HTML5 ouput.